Before rough cutting the buttplate to size, it should be temporarily attached to the stock with counterbored
625" long and requires a very precise counterbored
through-hole in the center.
With tile bolt closed, the chambered case bead is enclosed by the counterbored
bolt face, the chamber wall of the barrel and the front of the upper receiver that surrounds the barrel shank--all of which are steel.
It's not a bad idea to have the conversion done, considering that the chambers are counterbored
and it's deuced difficult to tell if the firing pin is resting on the rim of a cartridge.
Next, they counterbored
the ID with a special custom-made drilling tool in two progressively larger drill head sizes up to 2.
Drill the counterbored
holes for the walnut plugs to cover the drywall screws that hold the cross support (B).
Cylinder chambers aren't recessed for the cartridge rims, but the rear face of the cylinder is counterbored
a bit, so with the cylinder installed, it looks almost as if the chambers are recessed.
Some would travel through vents on the sides of the receiver ring, both adjacent to the counterbored
face of the bolt.
The grooved cylinder is counterbored
to better support and encase the head of the rimfire cases.
The back side needs counterbored
1/2" diameter to allow the recoil spring to fit in the rear of the striker.
The bolt has a counterbored
bolt head and two locking lugs with guide slot.
An anodized aluminum alloy tool plate with tapped and counterbored
holes and a precisely machined mounting surface are said to make attachment of tooling quick and easy.